1. Field of the Invention
The present invention relates generally to an image reader and more particularly to an image reader capable of adjusting the image density without prescanning or special sensors to detect the density of an original.
2. Description of Related Art
An image reader is used, for example, when an image of an original is electronically filed and read to be transmitted by facsimile, and the like. Conventionally, image readers using the linear charge coupled device (hereinafter abbreviated as CCD) have been provided.
Such an image reader has a platen glass to place the original and the CCD to scan the original. Reflection light from the original is converted, into an electric signal by the CCD. The electric signals are outputted as image data successively after being processed by a prescribed signal processing circuit.
When an image is read by the image reader, the density of the image to be formed is adjusted at an appropriate level. In order to effect this adjustment, conventionally the density of the original image has been previously read by prescanning, which is performed before the scanning for an actual image reading. The read signals are adjusted so that the density becomes near the reference level. Other than the above described method for adjustment, sensors for detecting the density of the original image are used. The sensors carry out the density detection of the image. The image signals are adjusted based on the obtained density.
As described above, in the conventional image readers, prescanning or special apparatuses such as sensors for detecting density must be provided for adjusting the density of the image. Consequently, it takes much time for density adjustment and the image reader becomes expensive.